| 摘要 |
PURPOSE:To suppress reflected light from a wall in low level and improve the measurement precision of a particle speed by forming a recessed part in a wall facing an optical window where the wall is irradiated with a laser light beam, and slanting the internal surface of the recessed part to the laser light source. CONSTITUTION:An opening 1A is provided at part of the wall 1 which constitutes a flow passage. A transparent member 2 is fitted in the opening 1A to constitute the optical window 3. Then, the recessed part 6 is formed in the internal wall surface of the wall 1 forming the flow passage. The internal surface 6B of the recessed part 6 slants while becoming wider inwardly, and the bottom part 6C is formed slantingly to the laser light beam 5. The laser light beam 5 emitted by a laser light source 4 is condenced on a point of and then diverged to reach the internal wall surface 1B of the wall 1. The laser light 5 guided into the recessed part 6 is reflected inwardly. |
